(1) Field of the Invention
This invention relates to the preparation of N-.alpha.-alkoxyethyl-carboxylic acid amides from dimethyl acetal and a carboxylic acid amide such as acetamide and to the preparation of secondary N-vinyl carboxylic acid amides such as N-vinyl acetamide therefrom.
(2) Description of the Prior Art
Gless et al, U.S. Pat. No. 4,018,826 relates to a process for preparing poly(vinyl amine) salts. An intermediate product is N-vinyl acetamide which is obtained via the following steps:
(a) reacting acetaldehyde with at least two stoichiometric equivalents of acetamide in the presence of a strong acid catalyst to yield ethylidene-bis-acetamide;
(b) decomposing the ethylidene-bis-acetamide in the presence of an inorganic oxide surface catalyst under essentially neutral pH conditions to yield a decomposition product; and
(c) separating N-vinyl acetamide from this decomposition product.
These reactions can be illustrated by the following schematic: ##STR1##
The final reaction mixture, i.e., the mixture of N-vinyl acetamide with acetamide, contains relatively poor yields of the desired N-vinyl acetamide and requires extensive purification to isolate the N-vinyl acetamide.
Hartwimmer et al, U.S. Pat. No. 3,377,340, relates to a process wherein N-vinyl compounds of the general formula: ##STR2## in which R.sub.1 and R.sub.2 each represents an alkyl group or R.sub.1 and R.sub.2 can be linked with each other as a ring while forming an alkylene group which may be substituted by alkyl groups, and R.sub.3 and R.sub.4 represent hydrogen atoms or alkyl groups, can be prepared by catalytic splitting of N-(.alpha.-alkyoxyalkyl)-compounds of the general formula: ##STR3## in which R.sub.1, R.sub.2, R.sub.3 and R.sub.4 have the meanings given above and R.sub.5 represents an alkyl group, by heating them in liquid phase in the present of surface-active, insoluble substances which promote a weakly acid reaction.
The N-(.alpha.-alkoxyalkyl)-compounds disclosed as starting compounds can be prepared by reacting open chain or cyclic carboxylic acid amides which carry at least 1 hydrogen atom capable of being substituted on the nitrogen atom, with acetals or hemiacetals the aldehyde component of which contains more than 1 carbon atoms, or with acetal or hemiacetal-forming components in the presence of acid catalysts. However, no disclosure is made of the preparation of the specific N-vinyl amides of this invention, the specific intermediate ether amides from which they are obtained, or the critical disproportionation reaction to produce such intermediates.